Catalytic converters-metal foil material for use herein, and a method of making the material

Abstract

A metal foil substrate material with improved formability properties for catalytic converters and a method of making the material in which layers of ferritic stainless steel and aluminum are solid state metallurgically bonded together forming a composite material. Such composite material is further rolled to an intermediate foil gauge and then subjected to a thermal in situ reaction to form a resulting uniform solid solution foil material with superior high temperature corrosion resistance. This uniform solid solution material is then rolled to the final foil gauge.

We claim: 
     
       1. A method for making a foil substrate material with excellent formability having various metal constituents for catalytic converters comprising he steps of: providing a layer of a first material chosen from the group consisting of chromium containing ferrous metals and aluminum and aluminum alloys, sandwiching said layer of first material between first and second layers of a second material chosen from the group consisting of chromium containing ferrous metals and aluminum and aluminum alloys not chosen for the first material, metallurgically bonding said layers together by reducing thickness of said layers thereby forming a multilayer composite material of said first and second materials, reducing thickness of the composite material to an intermediate thickness between a starting thickness after bonding and a finish thickness; said intermediate thickness being chosen such that said foil substrate material possesses limited anisotropy of its mechanical properties, heating said composite material in situ at a temperature between 900° C. and about 1050° C. for a sufficient period of time to cause diffusion of various metal constituents of said layers throughout the composite material thereby providing a uniform solid solution material and rolling said uniform solid solution material to said finish thickness.   
     
     
       2. The method according to claim 1 wherein said heating of said multilayer composite material is to a temperature of less than about 1000° C. 
     
     
       3. The method according to claim 1 wherein said first material is a ferritic stainless steel and said second material is aluminum. 
     
     
       4. The method according to claim 1 wherein said heating comprises maintaining said multilayer composite material at peak temperature for between about 1 and 60 minutes. 
     
     
       5. The method according to claim 1 wherein a chemical composition of the uniform solid solution material is between 18 and 22 wt. percent Cr, at least 5 wt. percent Al and the balance Fe. 
     
     
       6. The method according to claim 5 wherein the chemical composition further includes rare earth metals as a minor constituent. 
     
     
       7. The method according to claim 6 wherein said minor constituent of rare earth metals is between 0.01 and 0.10 wt. percent. 
     
     
       8. The method according to claim 7 wherein the chemical composition further includes a content of S of less than 0.003 wt. percent. 
     
     
       9. The method according to claim 1 wherein said intermediate thickness is between 0.002 of an inch and 0.008 of an inch. 
     
     
       10. The method according to claim 9 wherein said finish thickness is between 0.0010 of an inch and 0.0025 of an inch. 
     
     
       11. The method of claim 1 wherein the reduction from said intermediate thickness and said finish thickness is between about 50 percent and 75 percent. 
     
     
       12. The method according to claim 1 further including annealing said uniform solid solution material after rolling to finish thickness to recrystallize the microstructure. 
     
     
       13. A method for making a substrate material having various metal constituents for use in catalytic converters comprising the steps of: providing a metallurgically bonded multilayer composite material with one or more of the layers chosen from the group consisting of stainless steel materials and aluminum materials and at least another layer being chosen from said groups but not the material chosen for the one or more layers, reducing the thickness of the composite material to an intermediate thickness of between about 0.002 of an inch and 0.008 of an inch, heating said composite material at a temperature and for a sufficient period of time to cause diffusion of various metal constituents of said layers throughout the composite material thereby providing a uniform solid solution material, and rolling said uniform solid solution material to a finish thickness of between about 0.0010 of an inch and 0.0025 of an inch wherein said intermediate thickness is chosen such that said substrate material possesses at least one of the properties chosen from the group consisting of limited anisotropy in its mechanical properties and a surface roughness of not greater than about 5 micro inches.   
     
     
       14. A method for making a foil substrate material having various metal constituents for catalytic converters comprising the steps of: providing a layer of a first material chosen from the group consisting of chromium containing ferrous metals and aluminum and aluminum alloys, sandwiching said layer of first material between first and second layers of a second material chosen from the group consisting of chromium containing ferrous metals and aluminum and aluminum alloys not chosen for the first material, metallurgically bonding said layers together by reducing thickness of said layers thereby forming a multilayer composite material of said first and second materials, reducing thickness of the composite material to an intermediate thickness between a starting thickness after bonding and a finish thickness; said intermediate thickness being chosen such that said foil substrate material possesses a surface roughness of not greater than about 5 micro inches, heating said composite material in situ at a temperature between 900° C. and about 1050° C. for a sufficient period of time to cause diffusion of various metal constituents of said layers throughout the composite material thereby providing a uniform solid solution material and rolling said uniform solid solution material to said finish thickness.   
     
     
       15. The method of claim 14 wherein the reduction from said intermediate thickness and said finish thickness is between about 50 percent and 75 percent. 
     
     
       16. The method according to claim 14 further including annealing said uniform solid solution material after rolling to finish thickness to recrystallize the microstructure.